The present invention relates to a system and method for whitening teeth, and, more particularly, to a system and method employing the use of heat and a delivery system which provides catalytic action thus accelerating the action of a bleaching medium.
Whiter teeth are desired for cosmetic reasons, and several processes to accomplish this have been described in the prior art. These processes have always included the use of bleaching gels or solutions containing various concentrations of hydrogen peroxide (H2O2) or carbamide peroxide (CH6N2O3), which on an equal molar basis contains 35% H2O2 (by weight) which is released from activation by water or other sources such as heat or light. The degree of whitening provided by these processes increases with (a) peroxide concentration, (b) time of contact between the reacting species of peroxide and the tooth enamel surface, (c) diffusion rate into the dentine layer, (d) a favorable structure (texture) of tooth surface, and most importantly, (e) the rate of activation of the gel in terms of generating available peroxide (H2O2) and/or its reactive species (OH and O). Due to its chemical structure, the peroxide must produce transient species such as OH and O before the final products, H2O and O2, are generated by the following mechanism, 2 H2O2xe2x86x924OHxe2x86x922H2O+2Oxe2x86x922H2O+O2. The presence of these active transient species (radical OH and atomic oxygen O) play the most important role in the whitening process due to their higher reactivity. In other words, two peroxide molecules must break down to four OH molecules, which react to produce two water (H2O) molecules and two atoms of oxygen. The final step is the recombination of atomic oxygen into molecular oxygen.
In most cases, tooth whitening is accomplished with custom fitted plastic trays filled with bleaching gels (known as xe2x80x9ctake home traysxe2x80x9d) which are worn for one to several hours a day or overnight over extended periods of time such as several weeks or months before a satisfactory level of whitening is realized. Gel activation by light from laser sources or arc lamps in several regions of the electromagnetic spectrum, including infrared, visible, and ultraviolet, have been introduced with various and ambiguous levels of success due to: (a) lack of fundamental understanding of the mechanism involved in the whitening process, (b) lack of control in terms of the density of delivered energy, (c) the fraction of the energy absorbed by gel or absorbed by teeth, (d) shadowing effects, and (e) the necessity for prolonged periods of treatment if one tooth is treated at a time. (See, e.g., U.S. Pat. Nos. 4,952,143 and 4,661,070.)
Furthermore, some of the peroxide concentrations used (from 15% up to 30% H2O2) require effective gum isolation in order to prevent tissue burns. There is also a lack of information on the temperature that is generated by the light source and lack of temperature control. These factors can lead into gum burns, tooth sensitivity after the treatment, and possible long-term effects that are presently unknown.
Another method, U.S. Pat. No. 4,983,381, involves the use of applying heat directly to the teeth with a thermocube or plate, which covers the teeth. This method is difficult to implement and requires soft tissue isolation and protection due to high concentrations of H2O2 (30-70%) as well as requiring many steps and high temperatures (up to 55xc2x0 C.). This design is also problematic because its close fit on the teeth does not allow enough volume for whitening gel. It also requires custom made plates (upper and lower arches) for each person.
Still another method, U.S. Pat. No. 5,927,981, utilizes a high temperature chamber for producing a high temperature (60xc2x0 C.). In this method, a bleaching vapor is directed to the teeth from the chamber. This process is difficult to implement and exposes the recipient to unnecessary safety risks due to both the tooth pulp and the gums (if not isolated) being exposed to high temperatures. In addition, its whitening effectiveness is uncertain and further complicated by the fact that the transient species OH and O may no longer be present in the xe2x80x9cbleaching vaporxe2x80x9d when it reaches the teeth due to the length of travel.
The present invention provides a process which has the following advantages over the prior art: (a) lower peroxide concentrations (16% to 20% carbamide or 5 to 10% H2O2); (b) no gum isolation is required; (c) within one hour it can provide up to eleven shades of improvement, depending on age and level and type of coloration; (d) it provides greater comfort to recipient than take home trays or light activated whitening procedures; (e) it requires less peroxide over the course of the treatment than xe2x80x9ctake home trays;xe2x80x9d and (f) it is safer than the light activation methods, especially those using high intensity lasers or other uncontrolled high intensity light sources, including those in the blue portion of the spectrum.
It should also be pointed out that this invention will accelerate the whitening process as well when the gel is confined by dentist-made take home trays or current office bleaching procedures which employ higher concentrations of hydrogen peroxide (30%) with isolation.
The present invention provides a safe and effective way for whitening teeth through a combination of new techniques, including a balanced and controlled delivery of activated bleaching medium. The present invention accelerates the action of the bleaching medium by increasing (a) the gel temperature; (b) the concentration of active peroxide species of the gel at the interface between the tooth surface and the attached gel; (c) the reaction rate between the active transient species (OH and O) of the peroxide and the coloring compounds in the teeth; and (d) the diffusion rate of the active species through the enamel. A heating wave is provided by a controlled thermal source which allows the temperature of the gel to reach a safe temperature range of 40xc2x0-42xc2x0 C. on the tooth surface. The heating is also controlled by a combination of state of the art devices which control the temperature to xc2x11xc2x0 C. or on a simpler approach by heat transfer.
In a first embodiment, the device includes a heating element embedded into an aluminum (or other metal or conductive material) cylinder referred to as a xe2x80x9cheat sinkxe2x80x9d which is thermally insulated from the atmosphere with a plastic coating, highly insulating Styrofoam composite, or other insulator. The temperature of the heat sink is controlled and maintained at a level of 50xc2x0-65xc2x0 C. so that a controlled, constant amount of thermal energy flows into a mouthpiece. The mouthpiece is made from metal, a metal matrix composite, or other thermally conductive material. The mouthpiece preferably includes a metallic substructure with a plastic/organic filler and a low conductivity coating or an open cell foam cover.
The heat sink temperature is controlled so that the temperature of the mouthpiece and the gel does not exceed a preset level (about 41xc2x0 C.xc2x11xc2x0). In case this temperature is exceeded in an electrically-powered embodiment, a safety thermocouple at the base of the mouthpiece automatically shuts off the power of the control box. For added safety, the heating element is electrically insulated from its case by ceramic cement and the case is also insulated from the heat sink by another layer of cement. The exteriors of heat sink and the mouthpiece are further insulated by plastic or Styrofoam coatings, thus providing a third level of safety. In addition, the demand of electric current(of the 30 watt heater at 120 V) is low and is limited to 0.25 amperes.
The increased effectiveness and speed of the whitening process is due to the faster generation and mobility of H2O2 in the peroxide gel, the decomposition of H2O2 to OH and O, the enhanced diffusion rate into the tooth as well as the enhancement of the reaction rate between the active peroxide species (which can be radicals of OH or atomic oxygen O) and the compounds on the enamel and dentine responsible for the stains and coloration. It is the change in the molecular state and bond structure (from double to single carbon bonds) of the coloring compounds which accounts for the lighter color, as well as the removal of stain compounds from the enamel surface.
The mouthpiece of the present invention is preferably made of a metal matrix composite consisting of a high conductivity, high heat-capacity metal skeleton (e.g., aluminum, copper, steel or other conductive alloy) that is surrounded by or impregnated with an open cell, porous, flexible foam. The mouthpiece may also be covered with a perforated plastic material. One important feature of this invention is based on the heat flow delivery from the heat sink, which is kept in the range of 50xc2x0-70xc2x0 C. (depending on the relative size of heat sink to mouthpiece), to the metal matrix composite and is designed so that the foam temperature does not exceed levels of comfort or safety, which is in the vicinity of 41xc2x0 C.
The method of the present invention controls the flow of thermal energy from a heat sink in order to provide thermal activation of bleaching gels. It accelerates the reaction of peroxide active species with pathological and normal colorations thus resulting in a faster whitening process via controlled heat flow, enhanced catalytic H2O2 decomposition by the metal mouthpiece and the fast transfer of reactionary ingredients through the open cell foam to the teeth. The advantages of the proposed methods are as follows: (a) temperature control at the base of the mouthpiece ensures safety by protection from overheating higher than 41xc2x0 C., which is an acceptable safe level; (b) the conductive portion of the mouthpiece is isolated from the flesh of the mouth and the teeth; (c) it allows use of gels with lower peroxide concentrations which do not require protection and/or isolation of the gums through the application of coatings; (d) it works with a variety of hydrogen peroxide and/or carbamide peroxide gels, both hydrous and non-hydrous, the latter being more effective; (e) it provides a reservoir of peroxide sufficient to last at least a 30-minute treatment, to be repeated two or three times with new gel for best results; (f) the energy flow created by the heat sink as well as the construction of the mouthpiece provide the necessary balance required for the safety of the system; and (g) the flexible foam allows one size to fit all and its open cell structure allows easy transfer of more reactive species to travel from the metal side of the mouthpiece, which is hotter, to the tooth surface without raising the temperature of the tooth itself. This non-equilibrium event allows for even faster whitening results.
Other useful features of this invention include the fact that the metal component of the mouthpiece does not require plaster models to be made (to custom fit to the teeth) because it is large enough to fit most, if not all, mouth sizes due to the rigid metal front wall and the flexible foam or plastic back wall which provides the desirable fit around the teeth of any size or geometry. The construction of the mouthpiece is such that one mouthpiece can treat both upper and lower teeth simultaneously. The fact that the mouth is closed during treatment provides greater comfort to the recipient of the treatment, as compared to other methods based on light activation where the mouth is forced open with a lip retractor during the entire procedure. For several reasons (including safety and sanitary reasons), all or a portion of the metal matrix mouthpiece is designed to be disposable, such that it can be discarded at the end of the procedure.